The present invention relates to a mechanical fancy seam sewing machine with a cam set for controlling needle and feeding movements.
For sewing complicated fancy seams, such sewing machines are provided with arrangements for automatic control of stitch width, stitch field and feeding. For setting the initial position of the stitch and the stitch field, the sewing machine is equipped with a manual control unit which possibly is a combination control (e.g., a double knob) used for setting of several fancy seams. As to the setting of the stitch width and the zigzag pattern, this is preferably made by a separate control. Such a mechanism for controlling positions and movements in respect to several different units in the machine required that all the interior space in the machine be occupied. Such a machine is described in detail, for example, in Swedish Patent Spec. SE-P-212 970. In more recent sewing machine production, the requirements for lightness and compact performance of the machine have been raised, and therefore the adjustable zigzag mechanism is now built together with the ordinary fancy seam mechanism. This earlier construction described in SE-P-7303690-7 is known for its cam set, gear head and cam follower, which by way of link arms produce and transmit lateral movements to the needle. The lateral movement performed by only a cam disk and links is proportionally simple to effect, but when adjustment and proportionality of such a simply effected movement are also required, the problem with the needle control becomes more complicated. However, it is possible to make the construction somewhat simpler if the stitch field positions only need to be used when sewing straight seams in those positions. As to zigzag sewing machines in general, there is a tendency for an impaired feeding exactness in the middle of the stitch field as the tooth rows of the feed dog are situated widely apart on these machines. A possibility for obtaining better feeding exactness is to locate the stitch formation to some of the outer positions in the stitch field, where at least one tooth row is situated.